Field of Invention
The present invention relates to a light source optical system and a projection display apparatus employing the same.
Description of Related Art
In recent years, a projector has been developed that irradiates a fluorescent member with light flux emitted from a high-output laser diode (hereinafter, referred to as “LD”) as excitation light, and uses fluorescent light having a converted wavelength as source light. The brightness of such a projector can be increased by increasing the number of LDs or increasing the output intensity of a single LD.
However, when the intensity of light incident on the fluorescent member is increased, the optical density of a condensed light spot on a surface of the fluorescent member becomes excessively high, and this may lead to a decrease in light conversion efficiency.
United States Patent Application Publication No. 2012/0133904 discusses an arrangement in which two fly-eye lenses are provided next to an optical system configured to compress light fluxes from a plurality of LDs to uniform the optical density of a condensed light spot formed on the fluorescent member.
United States Patent Application Publication No. 2012/0133904 does not address an influence of variation that each LD has. More specifically, the parallelism of output light of an LD may vary depending on the LD. Therefore, a light source image formed near a second fly-eye lens in the arrangement discussed in United States Patent Application Publication No. 2012/0133904 may extend from a predetermined lens cell of the second fly-eye lens and enter an adjacent lens cell. As a result, the vignetting amount of light eclipsed by the optical element in the subsequent stage may increase and thereby negatively affect light use efficiency.
Further, it is not desirable to excessively increase the size of a lens cell with respect to a light source image to prevent the light source image from extending to an adjacent lens cell because this leads to an increase in overall size of the optical system.